As a result of research and production of nuclear weapons, large amounts of radioactive and heavy metal waste have been generated. This waste, termed "mixed waste" when it contains both radioactivity and other hazardous waste products, can have a tremendous impact on the environment and pose serious health risks to the general population. Hazardous waste products are also generated in hospitals, industries and other commercial facilities through a number of processes such as medical diagnostic testing, pharmaceutical and biotechnology research and pesticide research. In 1990, the United States produced over 4000 m.sup.3 of low level mixed waste including 2,840 m.sup.3 of liquid waste, 720 m.sup.3 of organic solvents such as chlorofluorocarbons (CFC's), corrosive organics and waste oil and 120 m.sup.3 of toxic metals. The Department of Energy (DOE) estimates that nuclear sites in 22 states will produce over 226,000 m.sup.3 of nuclear waste over the next two decades and that it will cost over $60 billion to treat or store this waste over a 75 year period. Thus, treatment and disposal of these wastes poses tremendous technical and environmental problems. To further complicate the situation, there is currently no available treatment method for technetium (Tc), a major waste product of nuclear facilities in the form of TcO.sub.4.sup.-.
The DOE reports that 399,000 m.sup.3 of high level radioactive waste are currently stored in large tanks at four locations: Hanford, Washington; Idaho National Engineering Laboratories (INEL), Idaho; Savannah River Site (SRS), South Carolina; and the West Valley Demonstration Project, New York. DOE is proceeding with plans to treat high level waste by processing it into a solid form (e.g. borosilicate glass) that would not be readily dispersable into the air or leachate into the ground or surface water. This treatment process is called vitrification. The vitrification process will generate approximately 29,000 canisters to be disposed of in a geologic repository.
Hazardous waste can easily contaminate its environment. For instance, over the past decade, several incidents have occurred in which radioactive material used in industrial devices has been mixed with scrap metal that was being recycled for steel production. This radioactive material (usually cesium) cannot always be detected because it is shielded by the container or scrap metal. Consequently, the radioactive dust can contaminate the steel facility's emission control system and the emissions dust. Steel producers in the U.S. are currently storing more than 10,000 tons of contaminated dust. In most cases, this waste contains both radioactivity and other hazardous materials such as lead, cadmium and chromium.
Disposal options for these materials have been limited, principally because of their mixed waste classification and the cost associated with disposal of large volumes of mixed or radioactive waste. Thus, because of high cesium concentrations, hazardous waste facilities may not provide suitable treatment protocols. Similarly, licensed low-level radioactive waste disposal facilities can only dispose of the cesium after the other hazardous waste has been removed. One procedure involves immobilizing radionuclides on solid matrixes and building barriers around the matrixes to minimize the spread or immobilization. However, hazardous waste can leach out of the barriers and permeate the surrounding environment.
Jeanjean et al. (1995) J. Radioanal. Nucl. Chem. 201(6)529-539 describe how the cations uranium, cadmium and lead can be sorbed to hydroxyapatite (HA). These authors postulate that these positively-charged elements are immobilized by occupying empty Ca2.sup.+ sites on the HA.
Thus, there remains a need for a safe and inexpensive method of treating hazardous waste, including materials such as Technetium, mixed waste and heavy metals.